Part of the fun of the game can be discovering new materials, so this guide is rich in spoilers that may decrease your fun. You have been warned.

Below is a table of alloys crossed with various reagents.

Below is a table of the statistics of the various materials.
For reference:
Pierce damage is increased by Dexterity, which also increases hit ratio %
Crush damage is increased by Strength, which also increases attack speed
Weight decreases attack speed, which is counteracted by Strength
Value is a multiplier which increases how much a finished piece is worth to a buyer.

For completeness, Intelligence/Strength/Dexterity affect what spells/shields/projectile weapons can be used, and how many times, as well as the damage produced thereby. Some use flat damage e.g. the Shuriken and AOE spells, and others scale based on stats, in example the Bow and Icebolt.

It's worth noting that the final unnamed material (that I personally dubbed Unobtainium) has stats of:
3 Pierce/3 Crush/25 Durability /30 Value

Which is the most valuable material in the game and cannot be alloyed with anything, but is outshone by Vibranium in raw stats, and Mithril, Forwardium and Treasurite have better stats technically, but Forwardium is functionally useless due to low durability, as it would really only be good for a hit or two.

All tools use the average of the raw stats, piercing and crush, as their base Power. Durability on all things, including tools, are important. Less durability on high value items will make NPCs come back more often, but will also make you spend more resources and decreased Power from low durability causes you to gain rapport slower. Rapport makes them sell to you for less.

My go-to for weapons is stacking dex/str Wolf-accessory armors, and going for Greatswords with preferably Vibranium. They are durable (and thus last a long time with low gradual damage drop-off), and pack a huge punch while balancing accuracy. Tank Armor with Str/Dex Vibranium Plate is the way to go. Use a plate shield when you expect heavy opposition.

Treasurite is my favored choice for non-tank armor; it has great stats in a pinch, and sells for a bundle. Cloth armor is actually very good for casters as you can stack huge amounts of INT and
combined with a high-damage greatsword, you can effectively just blast through an entire 9-enemy dungeon by spamming Icebolt.

Don't bother with enchanting; I've found it's functionally useless.

I hope you've enjoyed the guide and it's maybe saved you some time and frustration.